1. Field of the Invention
The present invention is directed to methods of forming filters by electroplating a metallic material onto a substrate, and in particular to methods of fabricating thermal ink jet printheads having electroplated filters integrally formed thereon.
2. Description of Related Art
A typical thermally actuated drop-on-demand ink jet printing system uses thermal energy pulses to produce vapor bubbles in an ink-filled channel that expels droplets from the channel orifices of the printing system's printhead. Such printheads have one or more ink-filled channels communicating at one end with a relatively small ink supply chamber (or reservoir) and having an orifice at the opposite end, also referred to as the nozzle. A thermal energy generator, usually a resistor, is located in the channels near the nozzle at a predetermined distance upstream therefrom. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. A meniscus is formed at each nozzle under a slight negative pressure to prevent ink from weeping therefrom.
Some of these thermal ink jet printheads are formed by mating two silicon substrates. One substrate contains an array of bubble generating heater elements and associated electronics (and is thus referred to as a heater plate), while the second substrate is a fluid directing portion containing a plurality of nozzle-defining channels and an ink-fill-hole for providing ink from a source to the channels (thus, this substrate is referred to as a channel plate). The channel plate is fabricated usually by orientation dependent etching methods.
Droplet directionality of ink expelled from these printheads can be significantly influenced by extrinsic particles finding their way into the printhead channels. In order to address this problem, a metal mesh filter has been laminated to an ink inlet side of the channel plate after assembly of the two wafers. Providing the laminated filter is a costly processing step. The filter must meet specific standards for corrosion resistance (some inks are corrosive) and usually are only available from vendors in specific sizes.
U.S. Pat. No. 4,561,789 to Saito discloses a thermal ink transfer printing system containing a thermal printing head comprised of a porous glass substrate which is covered with a polyimide thin film and consequently photoetched to produce a pattern of holes comprising an ink filter.
U.S. Pat. No. 4,639,748 to Drake et al discloses an ink jet printhead having an internal filtering system and fabricating process therefore. Each printhead is composed of two parts aligned and bonded together. One part contains a linear array of heating elements and addressing electrodes on one surface. The other part has a parallel array of elongated recesses for use as ink channels and a common ink supplying manifold recess in communication with the ink channels. The manifold recess contains an integral closed wall defining a chamber with an ink-fill hole. Small passageways are formed in the internal chamber walls to permit passage of ink therefrom into the manifold. Each of these passageways have smaller cross-sectional flow areas than the nozzles to filter the ink, while the total cross-sectional flow area of the passageways is larger than the total cross-sectional flow areas of the nozzles.
U.S. Pat. No. 4,864,329 to Kneezel et al discloses a thermal ink jet printhead having a flat filter placed over an inlet thereof by a fabrication process which laminates a wafer sized filter to aligned and bonded wafers containing a plurality of printheads. The individual printheads are obtained by a sectioning operation, which cuts through the two or more bonded wafers and the filter. The filter may be a woven mesh screen or preferably an electroformed screen with predetermined pore size. Since the filter covers one entire side of the printhead, a relatively large contact area prevents delamination and enables convenient leak-free sealing.
One problem associated with laminating a wafer sized filter mesh to an aligned and bonded wafer pair is that the filter mesh must be diced through when separating the multiple printheads from the bonded wafers. This damages the dicing blades, reducing their useful life, and can also cause delamination of the filter mesh from edges of the printheads.
U.S. Pat. No. 4,589,000 to Koto et al discloses a drop-on-demand ink jet printer which includes an integral ink jet head and ink jet container. An ink supply port includes a filter (see FIGS. 17-25). The filter is mechanically secured to a substrate by heat, and can be prepared by electroforming a nickel sheet.
U.S. Pat. application No. 07/624,390 to Michael R. Campanelli et al, filed Dec. 6, 1990, discloses an ink jet printhead having an integral membrane filter formed over the inlet of a channel-containing portion thereof. The integral membrane filter is formed on a channel wafer after it is anisotropically etched, and prior to mating with a heater plate wafer. A photopatternable layer is deposited over an etch resistant masking layer and exposed, patterned and developed to establish the mesh filter. In another embodiment, a side of the channel wafer not patterned and etched is heavily doped to increase the robustness of the membrane filter by functioning as an etch stop. This doped region beneath the patternable layer is then etched using the membrane filter as a mask to open the filter pores through the doped layer portion of the channel wafer.
Unlike U.S. Pat. application No. 07/624,390, the present invention fabricates filters from electroplated metallic material. Additionally, some metallic materials, such as, for example, gold are resistant to corrosion by many inks.
One problem associated with thermal ink jet technology is the sensitivity of ink droplet directionality to particles in the ink. Print quality is directly related to accurate placement of the ink droplets on a recording medium, and droplet directionality determines the accuracy of the ink droplet placement. It has been demonstrated that higher print quality is achieved with particulate-free ink sources and the degree of particulate-free ink is related to how close the final filtration of the ink is to the ink jet printhead. One source of particulate contamination is the manufacturing environment itself. At least a partial solution to particulate-induced misdirectionality problems is to construct the entire transducer structure in a clean environment. However, complete particle-free environments are not practical. This invention solves the problems of particle contamination during the fabrication of an ink jet printhead.